Organic acids, inorganic acids, ethanol and glycine are commonly used to prevent degeneration and improve the shelf-life of food products (Japanese Unexamined Patent Publication No. 56-109580, 57-43668, 58-138367).
Various foods have been screened for food-preserving substances in recent years, resulting in the discovery of such preservatives as polylysine, protamine, lysozyme, etc., in addition to synthetic chemical products; however, since these preservatives exhibit exceedingly strong antibacterial activity only against certain specific bacteria, they are not adequate as general food preservatives. In order to achieve satisfactory preservation it is necessary to add large amounts of these substances to foods, which is undesirable because of their high price which increases overall costs.
In addition to these substances, spices which have long been used in foods have also been reported to contain substances exhibiting antibacterial activity, but they also fail to fully satisfy the conditions required for food preservatives.
As mentioned above, preserving agents used in foods and drinks will preferably exhibit a continuous antibacterial effect for preservation over long periods with minimal amounts of addition, and when used in foods they must not impair their taste or texture.
Because widely used food preserving agents such as ethanol, glycine, organic acids and inorganic acids themselves have characteristic flavors and aromas, they cannot be added to foods and drinks in amounts required to provide adequate preservation effects. Also, natural substances such as polylysine, protamine and lysozyme have very weak antibacterial spectra, and thus while exhibiting strong antibacterial activity against specific bacteria they are not effective against most microbes responsible for degeneration of foods, and therefore cannot be considered as satisfactory preserving agents.